Tool mounting mechanism for a machine tool
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a tool mounting mechanism for a machine tool, particularly for a surface grinding machine, comprising a spindle sleeve, a tool spindle, e.g., a grinding wheel spindle, which is mounted without a backlash in said sleeve and has mutually opposite end portions protruding from said sleeve, a tool mounted on one of said end portions, a belt pulley mounted on the other of said end portions, a spindle carrier, which comprises at least two sleeve guiding means in which said sleeve is axially slidably mounted and one screw or a plurality of parallel screws (ball screws), which are connected to each other and to the sleeve by a crosspiece, is or are provided and is or are operable to axially adjust the spindle sleeve. 
     2. Description of the Prior Art 
     In known tool mounting mechanisms comprising a spindle sleeve, that spindle sleeve is provided on its outside peripheral surface with screw threads, which are in threded engagement with a nut, which is driven by a shaft for axially moving said sleeve. In accordance with German Patent Specification 894,969, an axial play between the nut and said screw threads is eliminated in that the nut consists of two parts, which are non-rotatably connected to each other and are axially movable relative to each other and axially forced toward each other by spring pressure. 
     Instead of the provision of such screw-threaded means for axially adjusting the spindle sleeve it is also known to axially adjust a spindle sleeve by means of a single ball or roller screw drive or by means of a plurality of parallel ball or roller screw drives, which are interconnected by a crosspiece. In that case it is essential to eliminate radial backlash. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to provide a tool mounting mechanism which is of the kind described last hereinbefore and which is provided with axial guiding means having no radial backlash. 
     In a tool mounting mechanism which is of the kind described first hereinbefore, that object is accomplished in that the sleeve is guided without a backlash because it is provided on its outside peripheral surface with at least three and particularly four axially extending ribs, each of which is axially movably mounted in two linear roller bearings provided in a spindle carrier on both sides of the rib. That arrangement ensures that any changes of the biasing forces acting on the spindle bearing means and the sleeve guiding means will not influence each other. Each of the axial ribs for guiding the spindle sleeve is secured to the peripheral surface of the sleeve on one side of the rib and on the other side of the ribs extends into a longitudinal recess of the spindle carrier between linear roller bearings provided on both sides of the rib. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a longitudinal sectional view showing a tool mounting mechanism which embodies the invention. 
     FIG. 2 is a transverse sectional view taken on line II--II in FIG. 1. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A preferred embodiment of a tool mounting mechanism which embodies the invention and is provided in a surface grinding machine will now be described with reference to the drawing. 
     The tool mounting mechanism shown in the drawing comprises a grinding wheel spindle 1 and a spindle sleeve 2. The grinding wheel spindle 1 is axially coupled to and rotatably mounted in the sleeve 2 by two rolling element bearing means 3 and 4 and has two end portions protruding from the sleeve 2 at opposite ends. One of said end portions of the spindle 1 carries a non-rotatably connected belt pulley 5, which is operatively connected by a belt 6 to a drive motor, not shown. The other end portion of the spindle 1 has secured to it a grinding wheel 7, which is axially adjustable by means of the sleeve 2 and the spindle 1. The sleeve 2 is axially adjustable by means of two parallel screws 8 and 9 and a crosspiece 10 connecting said screws 8 and 9 to the sleeve 2. The screws 8 and 9 consist of ball or roller screws and are operable via respective drives 11 and 12 by a drive motor which is not shown. 
     The spindle sleeve 2 is guided without a backlash by means of four longitudinal ribs 13 and 14, which are provided on the sleeve 2 adjacent to each end thereof. Each of the ribs 13 and 14 is secured on one side at 15 to the outside peripheral surface of the sleeve 2 and extends on the other side into an associated one of the axially extending recesses 16, which are provided in the two sleeve guiding means 17 and 18 provided in the spindle carrier adjacent to both ends of the sleeve 2. Each of the ribs 13 and 14 extends in the sleeve guiding means 17 or 18 between two linear roller bearings 19 provided on opposite sides of and serving to guide the rib 13 or 14. Adjacent to the linear roller bearings 19, the spindle carrier may be provided with lubricating nipples, which extend to the outside.